Quality of paper formation (minute uneven thickness) indicates the degree of fiber variance in paper sheet. The measurement of the degree of fiber variance takes into account the size and distribution of holes, flock distribution, and dust particle measurement. Generally, this has been checked by placing a sample sheet on an inspection box accommodating a light source to visually examine transparency distribution of the sheet.
This method, which is widely used in factories, is rather of subjective nature and results of the inspection varies according to each inspector since sufficient knowledge and long experience are required for such inspection.
For this reason, a formation meter as shown in FIG. 1 has been developed and is practically used. This formation meter comprises upper and lower heads b and c above and below the running paper a to be measured, the lower head c accommodating a light source d such as laser connected to an electric power source and a mirror f for irradiating the light from said light source d onto the paper a. The upper head b accommodates a photocell j for receiving the light e, which has passed through said paper a via a mirror g, a filter h and a lens i.
The light e from the light source d is irradiated on the paper a through the mirror f; the light e passing through the paper a enters the photocell j through a mirror g, a filter h and a lens i and is converted to voltage and is outputted. As shown in FIG. 2, the voltage value is indicated as formation index relative to the time.
When the formation index is measured, jet/wire ratio (J/W ratio) and the like are changed according to said formation index by judgment of an inspector to obtain better formation.